1. Field of the Invention
This invention relates to a picture converting device which converts picture information of a certain type to picture information of another type having different number of unit pictures per unit time, e.g., converting an NTSC (National Television System Committee) video signal (including 30 frame pictures per second) into picture information having 24 frame pictures per second.
2. Description of the Prior Art
Recently, there is broadly known a DVD which is a storage medium having a remarkably improved recording capacity. Now, it is assumed that a certain film (i.e., including 24 frame pictures per second) is recorded on a DVD. Normally, the picture information to be recorded on a DVD must be an NTSC video signal (i.e., including 30 frame pictures per second). Therefore, conventionally, the film or movie material including 24 frame pictures per second is converted into the video signal including 30 frame pictures per second by a so-called telecine conversion (also called as xe2x80x9c2-3 pull-down conversionxe2x80x9d). Subsequently, the video signal thus obtained is converted into digital picture signal constituted by plural pixels, and then the digital picture signal is recorded on a DVD by using a picture coding technique of so-called MPEG-2 (Moving Picture Expert Group-2) system. This will be described in more detail with referring to FIG. 1. FIG. 1 shows the manner of telecine conversion. By telecine converting the frame pictures 30 to 34 of the movie material including 24 frame pictures per second, the video signal is obtained which includes the pictures of first field 40, 42, 44, 46, 48, 50 and 52 and the pictures of second field 41, 43, 45, 47, 49 and 51. The pairs of field pictures 40 and 41, 42 and 43, 44 and 45, 46 and 47, 48 and 49, 50 and 51 constitute one frame picture in the video signal, respectively.
The above mentioned telecine conversion produces video signal including 30 frame pictures per second from the movie material signal including only 24 frame pictures per second, and hence there may occur the cases where an identical field picture is used twice as two field pictures (one of those two identical field pictures will be hereinafter referred to as xe2x80x9credundant field picturexe2x80x9d) and/or two field pictures originating from different picture and hence having different contents constitute one frame picture. The redundant field picture is one of the successive identical field pictures in the same phase, and in the example of FIG. 1 the field pictures 40 and 42, 45 and 47, 50 and 52 are the redundant field pictures, respectively. Here, the same phase means that both of the two field pictures belong to first field (odd field) or second field (even field). Also in FIG. 1, the field pictures of different contents, i.e., the field pictures 42 and 43, 44 and 45, constitute one frame picture. When the video signal obtained by the telecine conversion is recorded on a DVD according to MPEG-2 system, if the multiple redundant field pictures having the same contents are included in the video signal to be recorded, the MPEG-2 coding processing must be performed redundantly for those redundant pictures. Also, if two field pictures having non-analogous contents constitute one frame picture, there is less correlation between those two field pictures in the sense of MPEG-2 system. In both cases, the efficiency of coding according to MPEG-2 system may necessarily be degraded. In this view, if the telecine-converted video signal is recorded on a DVD, prior to the MPEG-2 coding processing, the video signal is converted again into the picture signal including 24 frame; pictures per second (i.e., the reverse telecine conversion is applied), and then coded by MPEG-2 system.
The conventional reverse telecine conversion is carried out as follows. First, for successive two field pictures of the same phase (i.e., first field or second field, odd field or even field), the luminance of each pixel of one field picture is compared with the luminance of the corresponding pixel of the other field picture so as to calculate the absolute value of the luminance difference of those corresponding pixels, and then the absolute values of the luminance difference are totalized for all pixels in one field picture to calculate the absolute value sum. Then, the absolute value sum are compared with a threshold value which is experimentally predetermined. If the absolute value sum is smaller than the threshold, it is determined that those field pictures are the redundant field pictures. Based on this result, the video signal is converted into the picture signal including 24 frame pictures per second, with eliminating the redundant fields thus detected.
In theory, the absolute value sum is zero in the case of redundant fields. However, in the case of actual video signal, the absolute value sum rarely becomes zero because of the noise and the like introduced during the telecine conversion processing, and the absolute value sum may also vary dependently upon the kinds of the original movie material and/or the condition during the telecine conversion. Therefore, in the above-mentioned method of detecting the redundant field pictures using a constant threshold, the redundant field picture cannot be correctly detected, and such incorrect detection of the redundant field pictures still deteriorates the coding efficiency by the MPEG-2 system.
In view of the above mentioned problem, an object of the present invention is to provide a redundant picture detecting device capable of accurately and stably detecting the redundant field pictures in a video signal, especially caused by the telecine conversion.
Another object of the present invention is to provide a picture converting device which performs picture conversion utilizing the above redundant picture detecting device and a picture recording medium for recording picture information produced by the picture conversion.
According to one aspect of the present invention, there is provided a redundant picture detecting device including: a calculator for calculating difference information indicating a difference between a unit picture and a subsequent unit picture having an identical phase for each of the unit pictures; a multiplier for multiplying the difference information of a unit picture preceding an object unit picture by a predetermined first constant to produce a preceding difference information and for multiplying the difference information of a unit picture following the object unit picture by the first constant to produce a following difference information, the first constant being greater than zero and smaller than 1; and a judging unit for judging that the object unit picture is a redundant picture if the difference information of the object information is smaller than both of the preceding difference information and the following difference information.
There is also provided a redundant picture detecting method including the steps of: calculating difference information indicating a difference between a unit picture and a subsequent unit picture having an identical phase for each of the unit pictures; multiplying the difference information of a unit picture preceding an object unit picture by a predetermined first constant to produce a preceding difference information and for multiplying the difference information of a unit picture following the object unit picture by the first constant to produce a following difference information, the first constant being greater than zero and smaller than 1; and judging that the object unit picture is a redundant picture if the difference information of the object information is smaller than both of the preceding difference information and the following difference information.
In accordance with the device or method thus configured, difference information indicating a difference between a unit picture and a subsequent unit picture having an identical phase is calculated for each of the unit pictures. Then, the difference information of a unit picture preceding an object unit picture is multiplied by a predetermined first constant to produce a preceding difference information, and the difference information of a unit picture following the object unit picture is multiplied by the first constant to produce a following difference information, wherein the first constant is greater than zero and smaller than 1. Then, it is judged that the object unit picture is a redundant picture if the difference information of the object information is smaller than both of the preceding difference information and the following difference information. Therefore, the redundant pictures can be correctly and reliably detected.
Further, the judging unit or step,may judge that the object unit picture is a redundant picture if the difference information of the object information is smaller than both of the preceding difference information and the following difference information and if the difference information of the object unit picture is smaller than the difference information of both the unit picture preceding the object unit picture and the unit picture following to the object unit picture. Therefore, the accuracy of the detection may be further improved.
Also, the judging unit or step may judge that the object unit picture is a redundant picture if the difference information of the object information is smaller than both of the preceding difference information and the following difference information and if the difference information of the object unit picture is smaller than a predetermined second constant. Thus, the accuracy of the detection may be further improved.
According to another aspect of the present invention, there is provided a redundant picture detecting device including: a calculator for calculating difference information indicating a difference between a unit picture and a subsequent unit picture having an identical phase for each of the unit pictures; and a judging unit for judging that the object unit picture is a redundant picture if the difference information of the object information is smaller than both of the difference information of a unit picture preceding to the object unit picture and the difference information of a unit picture following the object unit picture.
There is also provided a redundant picture detecting method including the steps of: calculating difference information indicating a difference between a unit picture and a subsequent unit picture having an identical phase for each of the unit pictures; and judging that the object unit picture is a redundant picture if the difference information of the object information is smaller than both of the difference information of a unit picture preceding to the object unit picture and the difference information of a unit picture following the object unit picture.
In accordance with the device and method thus configured, difference information indicating a difference between a unit picture and a subsequent unit picture having an identical phase is calculated for each of the unit pictures. Then, it is judged that the object unit picture is a redundant picture if the difference information of the object information is smaller than both of the difference information of a unit picture preceding to the object unit picture and the difference information of a unit picture following the object unit picture. Therefore, the redundant pictures can be correctly and reliably detected.
Further, the judging unit or step may judge that the object unit picture is a redundant picture if the difference information of the object information is smaller than both of the difference information of a unit picture preceding to the object unit picture and the difference information of a unit picture following the object unit picture and if the difference information of the object unit picture is smaller than a predetermined second constant. Thus, the accuracy of the detection may be further improved.
In a preferred embodiment, the above device or method may be used when picture information, in which m unit pictures are to be displayed per second, is converted to picture information of different type in which n unit pictures are to be displayed per second, wherein m and n are natural numbers and m greater than n.
Preferably, the calculator or the calculating step may calculate a sum of absolute values of luminance differences between each pixel of the unit picture and each corresponding pixel of the subsequent unit picture for all pixels in the unit picture to obtain the difference information. By this, the detection can be made dependently upon the difference information which directly affects the field pictures actually displayed.
According to still another aspect of the present invention, there is provided a picture converting apparatus including: the above redundant picture detecting device and a converter for converting picture information, in which m unit pictures are to be displayed per second, to picture information of different type in which n unit pictures are to be displayed per second, with eliminating the redundant unit pictures based on the judgement result of the judging unit, wherein m and n are natural numbers and m greater than n.
There is also provided picture converting method including: the above redundant picture detecting method, and a step of converting picture information, in which m unit pictures are to be displayed per second, to picture information of different type in which n unit pictures are to be displayed per second, with eliminating the redundant unit pictures based on the judgement result of the judging step, wherein m and n are natural numbers and m greater than n.
In accordance with the above apparatus or method, the picture information can be efficiently converted with reliably eliminating the redundant pictures.
Further, there may be provided a picture storage medium on which picture information converted by the picture converting device or method described above is recorded.
The nature, utility, and further features of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiment of the invention when read in conjunction with the accompanying drawings briefly described below.